Fiber-reinforced thermoplastic compositions in which reinforcing fibers are combined with resin are excellent in mechanical characteristics and dimension stability, and thus used in a wide variety of fields, such as automobiles, airplanes, electric/electronic devices, toys, and home electronics. Carbon fibers among other reinforcing fibers have attracted attention in recent years because of their light weight, high strength, and high stiffness.
Also, thermoplastic resins have attracted attention in recent years as matrix resins for fiber-reinforced thermoplastic resin compositions. Among others, polyolefin-based resins, particularly a polypropylene resin which is low in cost, low in specific gravity, and excellent in properties such as moldability and chemical resistance, have attracted attention.
However, the polyolefin-based resin is low in polarity, and its interface adhesiveness to reinforcing fibers is thus inferior. Therefore, attempts have been conducted to improve the interface adhesiveness between reinforcing fibers and their matrix resin by surface treatment of the reinforcing fibers, application of a sizing agent, and the like.
Patent Document 1 describes a carbon fiber covered with polyacrylic acid. Patent Document 2 discloses a reinforcing fiber covered with sodium polyacrylate and polyacrylamide. Patent Document 3 discloses a reinforcing fiber sizing agent that contains a polymer, (A), with a (meth)acrylic ester monomer, (a), unit in which an acryloyloxy group or a methacryloyloxy group is bound to a secondary carbon atom or a tertiary carbon atom. Patent Document 4 describes carbon fibers provided with a (meth)acrylic-based polymer having an aminoalkylene group in the side chain thereof or an oxazoline group-containing polymer. All these patent documents intend to improve the interface adhesiveness between a carbon fiber and a matrix resin by providing the carbon fiber with a polymer having an affinity for polyolefin resin, although in each case, the resulting interface adhesiveness is insufficient.
In addition, various investigations have been carried out to provide a method for manufacturing a fiber-reinforced thermoplastic resin composition.
Patent Document 4 discloses a method for manufacturing a fiber-reinforced thermoplastic resin, where a reinforcing fiber obtained by providing the reinforcing fiber with a predetermined polymer and a molten thermoplastic resin are blended together so that the reinforcing fiber, the polymer, and the thermoplastic resin can be combined together in a predetermined proportion.
Patent Document 5 discloses a method for manufacturing fiber-reinforced thermoplastic resin moldings using a carbon fiber having a mass-average fiber length of 0.5 to 10 mm, and an orientation parameter of −0.25 to 0.25, where the method includes: (I) a step of heat-melting a thermoplastic resin contained in a molding material; (II) a step of placing the molding material in a die; (III) a step of pressurizing the molding material in the die; (IV) a step of solidifying the molding material in the die; and (V) a step of opening the die to take out a fiber-reinforced thermoplastic resin from the die.
Patent document 6 discloses a method for manufacturing a sheet-shaped product, where a binder mainly containing a nonflammable fibrous material and a thermoplastic resin and serving as main component and a slurry liquid containing other predetermined components is supplied to a running or rotating meshed or porous substrate diagonally at an angle of 5 to 60 degrees with respect to the surface of the substrate, followed by dehydration and drying.
The manufacturing method disclosed in Patent Document 4 only applies a (meth)acrylic-based polymer component to a fiber-reinforced web. No consideration is given to productivity, such as take-off properties in subsequent steps. Improvements in the manufacturing method have been required for wide use as fiber-reinforced composite material.
Any of the manufacturing, methods disclosed in Patent Documents 5 and 6 does not use any specific means for taking off a molding material, and thus requires much time and troublesome operations for its production. Improvements in the manufacturing method have been required for efficient production of fiber-reinforced thermoplastic resin compositions.